Running controller for automobile

ABSTRACT

A vehicle speed control apparatus for allowing a host vehicle trailing a preceding vehicle to accelerate and decelerate without causing discomfort to the host vehicle driver. While the host vehicle is trailing the preceding vehicle, the apparatus on board the host vehicle stores the speed of the preceding vehicle entering a curve ahead as well as a headway distance of the host vehicle to the preceding vehicle. Upon reaching the curve, the host vehicle is controlled by the apparatus to enter the curve at a speed not in excess of the stored speed of the preceding vehicle.

TECHNICAL FIELD

The present invention relates to a vehicle speed control apparatus forcontrolling the speed of an own vehicle relative to a preceding vehicle.

BACKGROUND ART

A variety of devices have been developed to alleviate burdens on thedriver of a running vehicle and to enhance driving safety.Illustratively, cruise control systems and like apparatuses forcontrolling vehicles running at a constant speed have already beencommercialized. Currently under development are driving controlapparatuses that measure by radar a headway distance and a relativespeed of a host vehicle with respect to a preceding vehicle so as to letthe host vehicle run while maintaining the headway distance or avoidcollision with the preceding vehicle. A cruise control system, once itscruise mode switch is turned on, allows the vehicle to maintain itsspeed until an operation such as the stepping on the brake pedal iscarried out to cancel the cruise mode.

One conventional headway distance maintaining system allows the hostvehicle to maintain the headway distance if there is a precedingvehicle, and activates a following control device to get into cruisemode based on an established speed if there is no preceding vehicle.Japanese Patent Laid-open No. Hei 8-192661 discloses a driving controlapparatus claimed to work as follows: if the host vehicle trailing thepreceding vehicle loses the latter from a radar range, the apparatussets as a target vehicle speed the vehicle speed in effect when thepreceding vehicle was lost. Thereafter, if a suitable reset operation isperformed during a predetermined period of time, an initially setvehicle speed is restored; if no reset operation is carried out, thetarget vehicle speed is established as a new vehicle speed.

One disadvantage of the above and other similar conventional apparatusesis that if the preceding vehicle entering a curve is captured by radar,the apparatus causes the host vehicle to start decelerating well beforethe curve is reached so as to keep the headway distance unchanged.Another disadvantage is that when the preceding vehicle startsaccelerating at the exit of a curve, the host vehicle behind it alsostarts accelerating even if the trailing vehicle is still negotiatingthe curve.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above circumstancesand provides a vehicle speed control apparatus allowing a host vehicletrailing a preceding vehicle along a curve to accelerate and deceleratein accordance with the configuration of the road.

In carrying out the invention, there is provided a vehicle speed controlapparatus comprising detecting means for detecting a headway distance, arelative speed and a direction of a host vehicle with respect to apreceding vehicle, and computing means for computing a speed of thepreceding vehicle based on an own speed and the relative speed of thehost vehicle. After the speed of the preceding vehicle transiting agiven point on a road is acquired and retained, the host vehicle iscontrolled to pass that point at a speed not exceeding the retainedspeed of the preceding vehicle. When passing the point in question, thehost vehicle may be controlled to run at a speed not exceeding theretained speed of the preceding vehicle while keeping the headwaydistance to the preceding vehicle from getting shorter than apredetermined value. If subject to a yaw rate of a predetermined minimumvalue, the host vehicle may be controlled to keep its own speed fromexceeding a maximum speed determined by the yaw rate. If the vehiclespeed control apparatus further comprises detecting means for detectingheadway distances and directions of the host vehicle with respect to aplurality of preceding vehicles, and if the plurality of precedingvehicles change their courses in the same direction, the apparatus maydetect the presence of a curve ahead of the host vehicle and may keepthe speed of the host vehicle entering the curve not in excess of thespeeds of the preceding vehicles. If the plurality of preceding vehicleschange their courses in different directions, the vehicle speed controlapparatus may control the speed of the host vehicle by getting roadinformation from an onboard navigation device to determine whether thedirectional change is attributable to the preceding vehicles headinginto road branches or changing lanes.

The inventive vehicle speed control apparatus above controls the hostvehicle entering a curve in a way that keeps its speed from exceedingthe speed of the preceding vehicle that entered the curve earlier. Thisprovides speed control of the host vehicle in keeping with theconfiguration of the road. Because the lateral acceleration of the hostvehicle is proportional to the product of the own speed and a yaw rateof the vehicle, the maximum vehicle speed may be set in accordance withthe yaw rate. This keeps the lateral acceleration of the host vehiclefrom exceeding a predetermined level, thus enhancing ride quality inkeeping with the road configuration. When the host vehicle is running amultiple-lane road, the inventive apparatus may detect a plurality ofpreceding vehicles changing their courses to ascertain the presence ofcurves and thereby allow the host vehicle to travel in accordance withthe road configuration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a vehicle speed control apparatus embodyingthe invention.

FIG. 2 is a schematic view showing a positional relation between a hostvehicle and a preceding vehicle.

FIGS. 3A and 3B are graphic representations of the speed of the hostvehicle varying with respect to that of the preceding vehicle.

FIGS. 4 through 6 are flowcharts of steps constituting specific flows ofcontrol in trailing mode.

FIGS. 7 and 8 are schematic views depicting positional relations betweenthe host and preceding vehicles as the host vehicle loses sight of thepreceding vehicle.

FIG. 9 is a flowchart of steps constituting a flow of control in effectwhen the host vehicle while negotiating a curve loses sight of thepreceding vehicle.

FIGS. 10 and 11 are schematic views indicating positional relationsbetween the host vehicle and a plurality of preceding vehicles.

FIG. 12 is a flowchart of steps constituting a flow of control of thehost vehicle trailing a plurality of preceding vehicles.

FIG. 13 is a schematic view illustrating a positional relation betweenthe host vehicle and the preceding vehicle as the latter's speed vectoris estimated.

FIGS. 14 and 15 are flowcharts of steps constituting flows of control inestimating the speed vector of the preceding vehicle.

FIG. 16 is a flowchart of steps constituting a flow of control in effectwhen information from a navigation device is utilized.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the invention will now be described withreference to FIGS. 1 through 15. FIG. 1 is a system block diagram of avehicle speed control apparatus embodying the invention. The vehiclespeed control apparatus comprises a main control unit 20 for drivingcontrol. The main control unit 20 is connected to a number ofcomponents: a radar device 10 capable of detecting headway distances,relative speeds and directions of a host vehicle with respect to aplurality of preceding vehicles; a vehicle speed sensor 11 for measuringan own speed of the host vehicle; a yaw rate sensor 12 for measuring ayaw rate of the host vehicle; and switches 13 making up an input deviceby which to input commands for starting and stopping driving control aswell as a target vehicle speed in cruise mode. Information from anavigation device 30 is also input to the main control unit 20. The maincontrol unit 20 incorporates a storage unit 16, a target vehicle speedand acceleration computing unit 17, a vehicle control unit 18, and adisplay content computing unit 19. The target vehicle speed andacceleration computing unit 17 computes a target vehicle speed andtarget acceleration based on the headway distance, the relative speedand the direction measured by the radar device 10, the own speed of thehost vehicle measured by the vehicle speed sensor 11, on the yaw ratemeasured by the yaw rate sensor 12, and on the settings of the switches13. Given a target vehicle speed and acceleration, the vehicle controlunit 18 computes command values destined for a throttle valve controller21, a transmission controller 22 and a brake controller 23, and outputsthe commands to the respective controllers. The settings of the switches13 and the computed results from the target vehicle speed andacceleration computing unit 17 and vehicle control unit 18 are fed tothe display content computing unit 19. Based on the received data, thedisplay content computing unit 19 displays on a display unit 29 drivingcontrol indications allowing the driver easily to verify the drivingstatus. The throttle valve controller 21 controls the opening of athrottle valve 24 in accordance with a command value from the vehiclecontrol unit 18. Similarly, the transmission controller 22 and brakecontroller 23 control a transmission 26 and a brake actuator 27respectively in keeping with command values supplied by the vehiclecontrol unit 18.

FIG. 2 is a schematic view explaining how the embodiment of theinvention operates in practice. FIG. 3A is a graphic representation ofthe speed of the preceding vehicle versus the own speed of the hostvehicle over distance with the embodiment in use. FIG. 3B is a graphicrepresentation of the speed of the preceding vehicle versus the ownspeed of the host vehicle in effect when a conventional headway distancecontrol apparatus is employed. In the situation of FIG. 2, the hostvehicle 1 trails the preceding vehicle 2. The radar device 10 on boardthe host vehicle 1 measures a distance R1, a relative speed Rdl and adirection θ₁ in relation to the preceding vehicle 2.

With the conventional headway distance control apparatus working asillustrated in FIG. 3B, the own speed of the host vehicle is controlledin synchronism with the speed of the preceding vehicle. Thus thepreceding vehicle and host vehicle travel at about the same speed V1 attime t3. In this case, the preceding vehicle passes point P3 at time t3and, by the time the host vehicle passes point P3 at time t4, thepreceding vehicle is traveling at a speed V4. It follows that thereoccurs a difference in speed (V3−V4) between the preceding vehicle andthe host vehicle passing point P3.

With the inventive apparatus working as depicted in FIG. 3A, thepreceding vehicle running at speed V1 passes point P1 at time t1 atwhich the host vehicle passes point Q1. The distance between the hostvehicle and the preceding vehicle is equal to the distance betweenpoints P1 and Q1. The speed of the preceding vehicle is computed fromthe own speed of the host vehicle and its relative speed with respect tothe preceding vehicle. The target vehicle speed and accelerationcomputing unit 17 computes a target vehicle speed and targetacceleration based on the difference between the speed of the hostvehicle and the preceding vehicle speed V1 at time t1, in such a mannerthat the host vehicle arriving at point P1 will run at speed V1, i.e.,the speed at which the preceding vehicle passed point P1 earlier. On thebasis of the target vehicle speed and target acceleration thus computed,the vehicle control unit 18 sends suitable command values to thethrottle valve controller 21 and transmission controller 22 as well asto an actuator controller in the brake controller 23 for deceleration sothat the host vehicle passes point P1 at speed V1. Likewise, when thepreceding vehicle accelerates, e.g., when the preceding vehicle ispassing point P2 at speed V2 at time t2, the host vehicle is passingpoint Q2. Given the difference between the own speed and the speed V2 ofthe preceding vehicle at time t2, the target vehicle speed andacceleration computing unit 17 computes a target vehicle speed andtarget acceleration accordingly. Based on the target vehicle speed andtarget acceleration thus computed, the vehicle control unit 18 sendsappropriate command values to the throttle valve controller 21 andtransmission controller 22 for acceleration so that the host vehiclearriving at point P2 reaches speed V2 at which the preceding vehiclepassed P2 earlier.

FIG. 4 is a flowchart of steps constituting a typical driving controlroutine carried out by the main control unit 20. In step 100, a check ismade to see if vehicle speed controlled driving mode is established bythe switches 13. In step 101, the own speed of the host vehicle ismeasured. In step 110, a check is made to see if the onboard radardevice 10 is keeping the preceding vehicle within its range. If thepreceding vehicle is out of the range of the radar device 10, step 111is reached in which the host vehicle is controlled so as to maintain atarget vehicle speed. If the preceding vehicle is kept within the rangeof the radar device 10, step 102 is reached in which a headway distance,a relative speed and a direction of the host vehicle in relation to thepreceding vehicle are measured by radar. In step 103, a check is made tosee if the direction of the preceding vehicle exceeds a predeterminedthreshold value. If the direction of the preceding vehicle is found tobe in excess of the threshold value, i.e., if the preceding vehicle isdeviating by a predetermined angle from the frontal direction of thehost vehicle, step 104 is reached in which the speed of the precedingvehicle passing a given point is obtained. In step 105, a target speedand target acceleration are acquired so that when the host vehiclereaches that point of the preceding vehicle at which the latter's speedwas measured, the own speed of the host vehicle will not exceed themeasured speed of the preceding vehicle. If in step 103 the precedingvehicle is judged to be in the frontal direction of the host vehicle,then step 107 is reached. Step 107 is carried out to obtain a targetvehicle speed and target acceleration such as to attain a suitableheadway distance to the preceding vehicle (e.g., distance to be coveredin two seconds by the host vehicle running at its own speed) on thebasis of the own speed, current headway distance and relative speed ofthe host vehicle. Given the target speed and acceleration values thusobtained, the main control unit 20 outputs suitable command values tothe throttle valve controller 21, transmission controller 22 and brakecontroller 23 in order to attain the target values. In the typicalroutine of FIG. 4, a directional change rate of the preceding vehiclemay alternatively be obtained following step 102. In that case, a checkis made in step 103 to see if the directional change rate of thepreceding vehicle is in excess of a threshold value. This modificationalso provides similar driving control.

Another typical driving control routine is described below withreference to FIG. 5. The steps leading up to step 105 are the same asthose in the flow of driving control in FIG. 4. In step 105, a targetspeed and target acceleration are obtained. In step 108, a check is madeto see if either the headway distance measured in step 102 or a headwaydistance expected to be brought about upon control execution is inexcess of a predetermined threshold value. If either of the headwaydistances is found to be in excess of the threshold value, i.e., if asufficient headway distance is judged to be secured, step 106 is reachedin which the controllers are supplied with appropriate command valuespursuant to the target vehicle speed and target acceleration. If neitherof the headway distances is judged to exceed the threshold value in step108, then step 109 is reached. In step 109, the target speed andacceleration values are reduced so that the headway distance will not beless than the threshold value. The reduced values are handed over tostep 106 in which the actuator controllers are fed with appropriatecommand values for attaining the target values.

Described below with reference to FIG. 6 is a typical control routinethat additionally measures the yaw rate of the host vehicle. Aftervehicle speed controlled driving mode is judged to be established instep 100, step 120 is reached in which the own speed and yaw rate of thehost vehicle are measured. As in the example of FIG. 4, a check is madein step 110 to see if the radar device 10 is keeping the precedingvehicle within its range. If the preceding vehicle is out of the rangeof the radar device 10, step 111 is reached in which the host vehicle iscontrolled so as to maintain a target vehicle speed. If the precedingvehicle is kept within the range of the radar device 10, step 102 isreached in which a headway distance, a relative speed and a direction ofthe host vehicle in relation to the preceding vehicle are measured. Instep 121, a check is made to see if the yaw rate of the host vehicle isin excess of a predetermined threshold value. If the yaw rate is foundto be in excess of the threshold value, i.e., if the host vehicle isjudged to be turning, then step 104 is reached. In step 104, the speedof the preceding vehicle is acquired on the basis of the own speed andrelative speed of the host vehicle. In step 105, a target speed andtarget acceleration are acquired so that when the host vehicle reachesthat position of the preceding vehicle which was in effect uponmeasurement of step 102, the own speed of the host vehicle will notexceed the measured speed of the preceding vehicle. In step 122, a checkis made to see if the target speed obtained in step 105 is below amaximum speed determined by the yaw rate. If the target speed is judgedto be in excess of the maximum speed, step 123 is reached in which thetarget vehicle speed and target acceleration are modified so that thevehicle speed will not exceed the maximum speed. On the basis of thetarget speed and acceleration values thus acquired, the actuatorcontrollers are supplied in step 106 with appropriate command values forattaining the target values.

Described below with reference to FIGS. 7, 8 and 9 is a typical controlroutine for use when the preceding vehicle is lost from the radar rangewhile the host vehicle is negotiating a curve.

In the situation of FIG. 7, the onboard radar device 10 measures thedistance R1, relative speed Rdl and direction θ₁ of the host vehicle 1in relation to the preceding vehicle 2. In the situation of FIG. 8, thepreceding vehicle 2 is out of the radar range. In these drawings, dottedlines represent measuring ranges of radar.

FIG. 9 is a flowchart of steps constituting the control routine for usein the situations of FIGS. 7 and 8. After vehicle speed controlleddriving mode is judged to be established in step 100, step 120 isreached in which the own speed and yaw rate of the host vehicle aremeasured. In step 110, a check is made to see if the preceding vehicleis caught within the radar range. If the preceding vehicle is keptwithin the radar range, step 102 is reached in which a headway distance,a relative speed and a direction of the host vehicle in relation to thepreceding vehicle are measured. In step 131, the speed of the precedingvehicle is computed and stored into the storage unit 16. In step 121, acheck is made to see if the yaw rate of the host vehicle is in excess ofa predetermined threshold value. If the yaw rate is found to be inexcess of the threshold value, i.e., if the host vehicle is judged to beturning, then step 105 is reached. In step 105, a target speed andtarget acceleration are acquired so that when the host vehicle reachesthat position of the preceding vehicle which was in effect uponmeasurement of step 102, the own speed of the host vehicle will becomeequal to the measured speed of the preceding vehicle. If in step 121 theyaw rate is judged to be below the threshold value, then step 107 isreached. Step 107 is carried out to obtain a target vehicle speed andtarget acceleration such as to attain a suitable headway distance to thepreceding vehicle (e.g., distance to be covered in two seconds by thehost vehicle running at its own speed) on the basis of the own speed,current headway distance and relative speed of the host vehicle. If instep 110 the preceding vehicle is judged to be out of the radar range,step 132 is reached in which the most recently stored speed of thepreceding vehicle is established as a target vehicle speed. If the yawrate is judged to be in excess of the threshold value, step 122 isreached; if the yaw rate is found to be below the threshold value, step106 is reached. In step 122, a check is made to see if the target speedobtained in step 105 or 107 is below a maximum speed determined by theyaw rate. If the target speed is judged to be in excess of the maximumspeed, step 123 is reached in which the target vehicle speed and targetacceleration are modified so that the vehicle speed will not exceed themaximum speed. In keeping with the target speed and acceleration valuesthus acquired, the actuator controllers are supplied in step 106 withappropriate command values for attaining the target values.

Described with reference to FIGS. 10 through 12 is a typical controlroutine for use when a plurality of preceding vehicles are caught withinthe radar range. In the situation of FIG. 10, the onboard radar device10 measures the headway distance R1, relative speed Rd1 and direction θ₁of the host vehicle 1 in relation to the preceding vehicle 2, as well asa headway distance R2, a relative speed Rd2 and a direction θ₂ of thehost vehicle 1 in relation to another preceding vehicle 3. In thesituation of FIG. 11, the onboard radar device 10 measures a headwaydistance R3, a relative speed Rd3 and a direction θ₃ of the host vehicle1 in relation to yet another preceding vehicle 4 running ahead of thepreceding vehicle 2.

FIG. 12 is a flowchart of steps constituting the control routine for usein the situations outlined above. After vehicle speed controlled drivingmode is judged to be established in step 100, step 101 is reached inwhich the own speed of the host vehicle is measured. In step 110, acheck is made to see if the radar device 10 is keeping at least onepreceding vehicle within its range. If no preceding vehicle is caughtwithin the radar range, step 111 is reached in which the host vehicle iscontrolled so as to maintain a target vehicle speed. If in step 110 atleast one preceding vehicle is found to be kept within the radar range,step 143 is reached. In step 143, a check is made to see if there are atleast two preceding vehicles. If two preceding vehicles are not foundwithin the radar range, step 102 is reached in which the headwaydistance, relative speed and direction of the host vehicle in relationto one preceding vehicle are measured. Step 102 is followed by step 107.If at least two preceding vehicles are detected in step 143, step 140 isreached in which the headway distances, relative speeds, and directionsof the host vehicle in relation to the plurality of preceding vehiclesare measured. In step 141, a check is made to see if the directions ofthe plurality of preceding vehicles including the immediately precedingvehicle are in excess of a predetermined threshold value. If thedirections of the preceding vehicles are judged to exceed the thresholdvalue, step 142 is reached in which the immediately preceding vehicle isselected and its speed is obtained. In step 105, a target speed andtarget acceleration are acquired so that when the host vehicle reachesthat position of the immediately preceding vehicle which was in effectupon measurement of the latter's speed, the own speed of the hostvehicle will not exceed the measured speed of the preceding vehicle. Ifin step 141 the directions of the plurality of preceding vehicles arejudged to be below the threshold value, or if in step 143 only onepreceding vehicle is judged to be present, then step 107 is reached.Step 107 is carried out to obtain a target vehicle speed and targetacceleration such as to attain a suitable headway distance to thepreceding vehicle on the basis of the own speed, current headwaydistance and relative speed of the host vehicle in relation to thepreceding vehicle. Given the target speed and acceleration values thusobtained, the main control unit 20 in step 106 outputs appropriatecommand values to the throttle valve controller 21, transmissioncontroller 22 and brake controller 23 in order to attain the targetvalues.

Described below with reference to FIGS. 13 through 15 is typical meansfor allowing the host vehicle to control its own speed by computing arelative speed vector of the preceding vehicle.

FIG. 13 shows a method for obtaining a speed vector and a yaw rate ofthe preceding vehicle. It is assumed that the frontal direction of thehost vehicle 1 is represented by the Y axis and the directionperpendicular to the Y axis at the radar position is denoted by the Xaxis. The headway distance and direction of the host vehicle measured byradar relative to the preceding vehicle are used as a basis foracquiring relative coordinates (x, y) of the host vehicle in relation tothe preceding vehicle. The coordinates are temporally differentiated toprovide a relative speed vector as a temporally differentiable functionof the headway distance R, relative speed Rd, and direction θ of thehost vehicle. A speed vector direction φ of the preceding vehicle isobtained in terms of polar coordinates of the relative speed vector. Asa result, a relative yaw rate ω of the preceding vehicle as viewed fromthe host vehicle 1 is acquired as a function of speed vector componentsand differential values of the components.

FIG. 14 is a flowchart of steps constituting a typical routine forcontrolling the own speed of the host vehicle through acquisition of thespeed vector and yaw rate of the preceding vehicle. The steps leading upto step 102 are the same as those in the flow of FIG. 9. In step 150, arelative speed vector of the preceding vehicle is obtained. In step 151,a relative yaw rate acquired from changes in the speed vector of thepreceding vehicle is added to the yaw rate of the host vehicle toprovide a yaw rate of the preceding vehicle. In step 152, a check ismade to see if the yaw rate of the preceding vehicle is in excess of apredetermined threshold value. If the yaw rate is judged to be in excessof the threshold value, step 105 is reached. In step 105, a target speedand target acceleration are acquired so that when the host vehiclereaches that position of the preceding vehicle which was in effect atthe previous speed measurement, the own speed of the host vehicle willbecome equal to the measured speed of the preceding vehicle. If in step152 the yaw rate is judged to be below the threshold value, the step 107is reached. Step 107 is carried out to obtain a target vehicle speed andtarget acceleration such as to attain a suitable headway distance to thepreceding vehicle on the basis of the own speed, current headwaydistance and relative speed of the host vehicle. In keeping with thetarget speed and acceleration values thus acquired, the main controlunit 20 in step 106 supplies the actuator controllers with appropriatecommand values for attaining the target values.

FIG. 15 is a flowchart of steps constituting a typical routine for usewhen the speed vector is utilized for control. The steps leading up tostep 151 are the same as those in the flow of FIG. 13, whereby the speedvector of the preceding vehicle is computed. In step 153, a check ismade to see if the host vehicle has reached that position of thepreceding vehicle which was in effect upon measurement in step 102. Whenthe host vehicle is judged to have reached the previously measuredposition of the preceding vehicle, step 154 is reached in which the yawrate of the host vehicle is measured. In step 155, a check is made tosee if the difference between the yaw rate of the preceding vehiclecomputed in step 151 and the yaw rate of the host vehicle measured instep 154 is in excess of a predetermined threshold value. If thedifference is judged to be in excess of the threshold value in step 155,that means the direction in which the preceding vehicle is runningdiffers from the frontal direction of the host vehicle. In that case,the host vehicle is stopped from following the immediately precedingvehicle. If in step 155 the difference in yaw rate between the precedingvehicle and the host vehicle is found to be less than the thresholdvalue, step 160 is reached. Step 160 is carried out to obtain a targetvehicle speed and a target headway distance on the basis of the ownspeed, current headway distance, relative speed, direction and yaw rateof the host vehicle. In keeping with the target values thus acquired,the actuator controllers are supplied in step 106 with command valuesfor attaining these target values.

FIG. 16 is a flowchart of steps constituting a typical routine for usewhen road information from a navigation device is utilized. The stepsleading up to step 104 are the same as those in the flow of FIG. 4. Instep 160, the main control unit 20 receives road information regardingthe current vehicle position from the navigation device 30. Given theroad information, a check is made in step 161 to see if road branchesexist near the host or preceding vehicle. If no road branches are judgedto exist, step 105 is reached. In step 105, a target speed and targetacceleration are acquired so that when the host vehicle reaches thatposition of the preceding vehicle which was in effect upon the previousspeed measurement, the own speed of the host vehicle will not exceed themeasured speed of the preceding vehicle. If road branches are judged toexist in step 161, then step 107 is reached. Step 107 is carried out toobtain a target vehicle speed and target acceleration such as to attaina suitable headway distance to the preceding vehicle on the basis of theown speed, current headway distance and relative speed of the hostvehicle. In keeping with the target speed and acceleration values thusacquired, the main control unit 20 in step 106 supplies the throttlevalve controller 21, transmission controller 22 and brake controller 23with command values for attaining the target values.

Industrial Applicability

As described, the embodiment of the invention measures and stores thespeed of the preceding vehicle as it passes a given point on the road.When passing the same point, the host vehicle is controlled by theembodiment to run at a speed not in excess of the stored speed of thepreceding vehicle. The embodiment thus allows the host vehicle enteringa curve to run at a speed not exceeding the speed of the precedingvehicle having entered the same curve earlier. This provides the hostvehicle with speed control such that its driver can follow theconfiguration of the road with a minimum of discomfort. Because the hostvehicle is allowed to run while estimating the speed vector of thevehicle running ahead, the host vehicle can trail the preceding vehiclecomfortably even along a complicated road configuration comprisingnumerous curves.

What is claimed is:
 1. A vehicle speed control apparatus comprising:detecting means for detecting headway distances, relative speeds anddirections of a host vehicle in relation to a plurality of precedingvehicles; detecting means for detecting a host vehicle speed; computingmeans fore computing speeds of said plurality of preceding vehiclesbased on said host vehicle speed and said relative speeds of said hostvehicles; and controlling means which, if said plurality of precedingvehicles are found turning in the same direction, then judges that saidhost vehicle is heading toward a curved road and controls at least oneof a throttle valve device, a transmission device and a braking deviceso that said host vehicle speed entering said curved road does notexceed the speed of the immediately preceding vehicle having enteredsaid curved road earlier.
 2. A vehicle speed control apparatuscomprising: detecting means for detecting headway distances, relativespeeds and directions of a host vehicle in relation to a plurality ofpreceding vehicles; detecting means for detecting a host vehicle speed;computing means for computing speeds of said plurality of precedingvehicles based on said host vehicle speed and said relative speeds ofsaid host vehicle; and controlling means which, if said plurality ofpreceding vehicles are found turning in different directions, thencontrols at least one of a throttle valve device, a transmission deviceand a braking device so as to maintain said host vehicle speed for apredetermined period of time.
 3. A vehicle speed control apparatuscomprising: detecting means for detecting headway distances, relativespeeds and directions of a host vehicle in relation to a plurality ofpreceding vehicles; detecting means for detecting a host vehicle speed;computing means for computing speeds of said plurality of precedingvehicles based on said host vehicle speed and said relative speeds ofsaid host vehicles; and controlling means which, if said plurality ofpreceding vehicles are found turning in different directions, thenacquires road information about a currently-taken road from a navigationdevice, said controlling means further determining a target speed ofsaid host vehicle based on the computed speeds of said plurality ofpreceding vehicles and on the acquired road information.
 4. A vehiclespeed control apparatus according to claim 3, wherein said roadinformation includes road branch information; wherein, if said roadinformation points to road branches ahead, then said controlling meansallows said host vehicle to trail the immediately preceding vehicle; andwherein, if said road information indicates absence of any road branchesahead, then said controlling means controls at least one of a throttlevalve device, a transmission device and a braking device so as tomaintain said host vehicle speed for a predetermined period of time. 5.A vehicle speed control apparatus according to claim 3, wherein saidroad information includes road lane information; wherein, if a one-sidedsingle-lane road is currently taken, then said controlling means allowssaid host vehicle to trail the immediately preceding vehicle; andwherein, if a one-side multiple-lane road is currently taken, then saidcontrolling means controls at least one of a throttle valve device, atransmission device and a braking device so as to maintain said hostvehicle speed for a predetermined period of time.
 6. A vehicle speedcontrol apparatus comprising: detecting means for detecting a headwaydistance, a relative speed and a direction of a host vehicle in relationto a preceding vehicle; trailing means for allowing said host vehicle totrail said preceding vehicle; detecting means for detecting a hostvehicle speed and a yaw rate of said host vehicle; computing means forcomputing a speed vector of said preceding vehicle with respect to saidhost vehicle on the basis of said relative speed and said direction;computing means for computing a yaw rate of said preceding vehicle onthe basis of changes in said speed vector; and comparing means which, ifthe yaw rate of said preceding vehicle passing a given point is judgedto be in excess of a predetermined value, then stores the yaw rate ofsaid preceding vehicle, said comparing means further comparing thestored yaw rate of said preceding vehicle with the detected yaw rate ofsaid host vehicle when said host vehicle reaches the point at which theyaw rate of said preceding vehicle was stored.
 7. A vehicle speedcontrol apparatus according to claim 6, further comprising controllingmeans which, if a difference between the yaw rate of said precedingvehicle and the yaw rate of said host vehicle is judged to exceed apredetermined value, then controls at least one of a throttle valvedevice, a transmission device and a braking device so as to stop saidhost vehicle from trailing said preceding vehicle and to maintain saidhost vehicle speed for a predetermined period of time.
 8. A vehiclespeed control apparatus according to claim 6, further comprisingcontrolling means which, if a difference between the yaw rate of saidpreceding vehicle and the yaw rate of said host vehicle is judged to bebelow a predetermined value, then stores a speed of said precedingvehicle passing a given point and controls at least one of a throttlevalve device, a transmission device and a braking device so that saidhost vehicle speed passing said point does not exceed the stored speedof said preceding vehicle.